Excitation system for dynamo-electric machines



March 15, 1938. E. scHROTER 2,111,408

EXCITATION SYSTEM FOR DYNAMOELECTRIC MACHINES Filed June 26, 1957Inventor: Erich Sohrbter,

b Wan 1 6? 9 Hi Attorney.

' Patented Mar. 15. 1938 EXCITATION SYSTEM FOR DYNAMO-ELE(Y TRICMACHINES Erich Sehriiter, Berlin-Charlottenburg 4, Germany, assignor toGeneral Electric Company, a corporation of New York Application June 26,1937,'Serial No. 150,557 In Germany October 17, 1936 4 Claims.

My invention relates to control systems and more particularly toexcitation systems for dynamo-electric machines.

In the control of alternating current dynamoelectric machines of theself-excited type, it is frequently desirable to furnish the excitingcurrent by means of electric valves which are energized from the machineitself. in many applications it is desirable to initiate the build-up ofvoltage of the machine during the starting operation without usingcomplicated and expensive auxiliary equipment. Heretofore sucharrangements have employed devices having movable parts to efiect thechange-over from the starting operation to the normal running operation.Some of the other prior art arrangementshave employed the residualmagnetism of the dynamo-electric machine to initiate the build-up ofvoltage during the starting operation, and this type of control hasnecessitated the employment of complicated and expensive auxiliaryequipment. In view of the above factors, there has been evidenced adecided need for improved excitation by employing only those elementsentirely electrical in nature and operation and in which the transitionfrom the starting operation to the normal running operation may beefiected smoothly without employing electro-mechanical devices.

0 It is an object of my invention to provide a electric machines.

It is another object of my invention to provide a new and improvedelectric valve system for energizing the field circuit of a self-exciteddynamo-electric machine of the synchronous typ It is a further object ofmy invention to provide a new and improved excitation system forSelf-excited dynamo-electric machines in which the build-up of voltageof the machine is initiated and maintained without employing expensiveand complicated apparatus and which avoids the above mentioneddisadvantages.

45 In accordance with the illustrated embodiment of my invention, 1provide a new and improved excitation system for a self-excitedalternating current dynamo-electric machine of the syna chronous type.The excitation system comprises 50 only elements entirely electrical innature and operation, such as electric valve means and associatedcontrol equipment. More specifically, main electric valve means areconnected petween an armature winding of the machine and a field windingof the machine to supply direct Furthermore,

new and improved excitation system for dynamo current thereto duringnormal continuous operation, and an auxiliary electric valve means isemployed to supply direct current to the field Winding from an auxiliarysource of alternating current to initiate the build-up of armature 5voltage of the machine to a value sufiicient to permit the main electricvalve means to supply the requisite direct current to the field Winding.The auxiliaryor control electric valve means is provided with a controlmember which 10 controls the conductivity thereof. The excitationcircuit includes a voltage divider which is energized from the auxiliarysource of alternating current and impresses an alternating voltage onthe control member of the auxiliary elec- 15 tric valve tending torender the electric valve conductive. The excitation circuit alsoincludes a rectifier which is energized in accordance with the armaturevoltage of the machine for impressing on the control member of theauxiliary electric valve a negative unidirectional biasing potentialwhich varies in accordance with the armature voltage and renders theauxiliary electric valve non-conductive when the armature voltageattains a predetermined value. The transition from the startingcondition of operation to the running condition is efiected withoutemploying movable parts and is accomplished in a smooth and reliablemanner.

For a better understanding of my invention, 0 reference may be had tothe following description taken in connection with the accompanyingdrawing, and its scope will be pointed out in the appended claims. Thesingle figure of the accompanying drawing diagrammatically shows anembodiment of my invention as "applied to an excitation system for aself-excited alternating current generator of the synchronous type.

Referring now to the single figure of the ac companying drawing, thereis represented dia- 40 grammatically an excitation circuit for analternating current dynamo-electric machine 9 of the synchronous typehaving an armature winding 2 and a field Winding 3. The machine [I maybe driven by any suitable prime mover such as an elastic fluid turbine43. Although in the particular arrangement shown in the single figure oithe drawing 1 have chosen to show my invention as applied to alternatingcurrent generator of the synchronous type, it is to be 5g understoodthat my invention in its broader aspects may he applied todynamo-electric machines generally in W 'ch is desired to effectenergization of one W g of a machine irom another Winding thereon Thearmature winding 2 of dynamo-electric machine I is connected to analternating current circuit 5.

An electric valve translating circuit including main electric valves 8and I and a transformer 8 is connected between the alternating currentcircuit 5, or the armature winding 2 and the field winding 3, and isconnected to supply direct current to the field winding 3 during thenormal or continuous operation of the dynamoelectric machine I. The mainelectric valves 6 and I are preferably of the type employing anionizable medium, such as a gas or a vapor, and each includes an anode9, a cathode I8, and a control member II which controls the conductivityof the associated discharge path. To control the energization of controlmembers II and hence to control the conductivities of electric valves 8and I, there is provided a control circuit I2 including a conventionalphase shifting arrangement such as the rotary phase shifter I3 and atransformer I4. The transformer I4 is arranged to impress alternatingvoltages on control members I I of electric valves 6 and I throughcurrent limiting resistances I5, and the trans former I4 may be of thetype designed to furnish arr-alternating voltage of peaked wave form, ifdesired. It is to be understood that the control circuit I2 may beeither manually or automatically operated and that I may employ anyconvention-a1 arrangement to effect this control automatically.Furthermore, it is to be understood that the circuit I2 may be arrangedto control the conductivities of electric valves 6 and 'I and hence tocontrol the excitation of the field winding 3 in accordance with apredetermined electrical condition such as the armature voltage of thedynamo-electric machine I,

As a means for initiating the build-up of arm-ature voltage of themachine I by supplying current to the field winding-3 during thestarting operation, I provide an excitation circuit I8 including anauxiliary source of current which may be a source of alternating currentIT and an auxiliary or control electric valve means I8.

The electric valve means I8 is preferably of the type employing anionizable medium and comprises an anode III, a cathode 28 and a controlmember 2I. A transformer 22 may be employed as an element of theexcitation circuit I6 and a switch 23 may be employed. to connecttransformer 22 to the auxiliary source of alternating current II. Tofurnish a voltage which tends to render the electric valve means I8conductive, I provide a voltage divider comprising resistances 24 whichare connected in series relation across the electric valve means I8 andwhich are con-, nected in series relation with a secondary winding ofthe transformer 22 and field winding 3 of dynamo-electric machine I. Acurrent limiting resistance 25 may be connected in series relation withthe control member 2I of electric valve means I8. As an agency forrendering the electric valve means I8 non-conductive after the armaturevoltage of the dynamo-electric machine I attains a predetermined value,I provide a transformer 28 which is connected to the alternating currentcircuit 5, a rectifier 21, a capacitance 28 connected across outputterminals of the rectifier 21 and a suitable impedance element, such asa resistance 29, which introduce in the excitation circuit a negativeunidirectional biasing potential the magnitude of which varies inaccordance with the armature voltage of machine I. The capacitance 28 ischarged by the rectifier 21 and operates to stabilize the negativeunidirectional biasing potential and to absorb extraneous transientvoltages which may be introduced in the excitation circuit from thealternating current circuit 5 or from the dynamo-electric machine I.

While for the purpose of explaining my invention I have chosen to showthe auxiliary source of current H as being alternating current, it willbe well understood by those skilled in the art that I may employ asource of direct current in conjunction with any conventional expedientfor effecting transformation of the direct current to alternatingcurrent to energize the excitation circuit I8. For example, a source ofdirect current and an electric valve inverter could be employed totransform the direct current to alternating current of a desiredfrequency to energize the excitation circuit I6.

The operation of the embodiment of my invention diagrammatically shownin the accompanying drawing will be explained when the dynamoelectricmachine I is driven by the turbine 4 to supply energy to the alternatingcurrent circuit 5. For the purpose of explanation, it is assumed thatthe dynamo-electric machine I is the only source of voltage connected tothe circuit 5, To initiate the operation of the system, the fieldstructure of the dynamo-electric machine I is, of course, rotated by theprime mover 4 and the switch 23 is moved to the closed circuit positionto impress across the anode I9 and cathode 2B of electric valve I8,through the field winding 3, an alternating voltage. There is alsoimpressed across the voltage divider, including resistances 24, analternating voltage. Since the voltage impressed on control member 2I ofelectric valve I8 through the voltage divider, including resistances 24,is in phase with the voltage impressed on the anode I9 thereof, theelectric valve I8 will operate as a half wave rectifier to transmitpulsating unidirectional current to the field winding 3 of machine I toinitiate the build-up of the armature voltage of the machine. As thearmature voltage of the machine I increases due to the build-up ofcurrent supplied to the field winding 3, there will be attained avoltage sufiicient to initiate discharges within electric valves 6 and Iso that these valves begin to function to supply current to fieldwinding 3. It is to be understood that since the transformer 26 isconnected to alternating current circuit 5, there will be introduced inthe excitation circuit I6, across resistance 28, a negativeunidirectional biasing potential which varies in accordance with thevoltage of the circuit 5 or in accordance with the armature voltage ofthe machine I. As the voltage increases, the negative biasing potentialwill also increase and at a predetermined value of armature voltage thenegative unidirectional biasing potential will be sufficient to renderineffective the alternating voltage provided by resistances 24 so thatthe electric valve I8 is rendered non-conductive.

It is to be understood that by the adjustment of the rotary phaseshifter I3 the energization of the field winding 3 may be controlled toeffect control of the terminal voltage of the machine I. One of theprincipal advantages of my invention is the facility with which thetransition from the starting operation to the continuous runningoperation is effected. In addition, if for any reason the electrictranslating circuit including electric valves 8 and I becomestemporarily defective so that the voltage of the alternatin currentcircuit 5 decreases below a predetermined value, the excitation circuitI6 will automatically function to supply field current to the machine 3.

While I have shown and described my inven tion as applied to aparticular system of connec= tions and as embodying various devicesdiagrammatically shown, it will be obvious to those skilled in the artthat changes and modifications may be madewlthout departing from myinvention, and I, therefore, aim in the appended claims to cover all,such changes and modifications as fall within the true spirit and scopeof my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In combination, a dynamo-electric machine aving a field winding andan armature winding, an electric'valve means connected between saidarmature winding and said iield winding for supplying direct currentthereto, an auxiliary source of current, a second electric valve meanshaving a control member for supplying direct current to said fieldwinding from said auxiliary source to initiate the build-up of armaturevolt-= age of said machine, means energized from said auxiliary sourcetending to render said second electric valve means conductive, and meansenergized in accordance with the voltage of said armature winding torender said second electric valve means non-conductive when the, voltageof said armature winding attains a predetermined value. 7

2. In combination, a'dynamo-electric machine having a field winding andan armature winding, an electric valve meansconnected between saidarmature winding and said field winding for supplying-direct currentthereto, an auxiliary source of current, a secondelectric valve meanshaving a control member for supplying direct current to said fieldwinding from. said auxiliary source to initiate the build-up of armaturevoltage of said machine, and a control circuit for energizing saidcontrol member including a voltage divider for impressing on saidcontrol member a voltage tending to render said second electric valvemeans conductive and means energized from said arma ture winding forproviding a biasing potential to render said second electric valve meansnon= conductive when the voltage of said armature winding attains apredetermined value.

3. In combination, a dynamo-electric machine having a iield winding andan armature wind= alternating current, a second electric valve meanshaving a control member for supplying direct current to said fieldwinding from Said auxiliary source to initiate the build-up of armaturevolt= age of saidmachine, a voltage divider connected across said secondelectric valve means and energized from said aurn'liary source forimpressing on said control member a voltage tending to rendersaid secondelectric valve means conductive, and means energized in accordance withthe armature voltage ofsaid machine for impressing on said controlmember a negative unidirectional biasing potential to render said secondelectric valve means non-conductive when the voltage of said armaturewinding attains a predetermined value.

in an excitation circuit for a dynamo-electrio machine of thesynchronous type having a field winding and an armature winding, thecombination of electric valve means interposed between said armaturewinding and said field winding for supplying direct current theretoduring normal operation, an auxiliary source of alternating current, asecond electric valve means connected between said amdliary source andsaid field winding for supplying direct current thereto to initiate thebuild-up of armature voltage of said machine, said second electric valvemeans having a control member for controlling the conductivity thereof,means energized from said auxiliary source comprising a voltage dividerfor impressing on said control member an alternating voltage tending torender said second electric valve means conductive, and means energizedin accordance with the armature voltage of said machine comprising arectifier for impressing on 4 said control member a negativeunidirectional biasing potential to render said second electric valvemeans non-conductive when the voltage oi said armature winding attains apredetermined value.

ERICK SCHRiiWR.

